1. Field of the Invention
The present invention is related to an optical element for emitting an incident light beam in a desirable direction, an optical deflection element for emitting a plurality of light beams having different incidence angles or different wavelengths from each other in different directions, and an optical multiplexing element for optically multiplexing a plurality of light beams having different incidence angles in the same direction. Further, the present invention is related to a scanning apparatus with employment of such an optical deflection element.
2. Description of a Related Art
Conventionally, as an optical element or an optical deflection element, passive elements such as a prism, a diffraction grating, a concave lens and soon have been utilized. Further, very recently, as an optical deflection element, active elements such as a diffraction grating using an acoust-optic effect and a galvano scanner have been employed.
In such a diffraction grating using the acoust-optic effect, by propagating a compression wave (for instance, an ultrasonic wave) through a medium such as glass, a refractive index is changed periodically, so that a light beam is emitted in different directions. In a galvano scanner, by vibrating a mirror by using a resonant head, a light beam is emitted in different directions.
However, since the passive elements such as the prism, the diffraction grating, and the concave lens have a small deflection angle at which a light beam is emitted from the passive element, a long optical path is necessarily required so as to separate the incident light beam into a plurality of light beams corresponding to incidence angles or wavelengths. Therefore, in order that the light beams having different incidence angles or different wavelengths are deflected in a wide range, a dimension of such a passive element itself must be increased, and also the entire optical apparatus must be made large so as to secure the long optical path. On the other hand, in the active elements such as the diffraction grating using the acoust-optic effect and the galvano scanner, although light can be deflected in a wide range, cost of the active element itself is expensive, and also the active element owns a slow response to the input signals.
Very recently, specific crystal (namely, photonic crystal) having a different optical characteristic from that of the conventional optical crystal has been effectively developed. The photonic crystal owns a crystal structure in which, within a first medium, a second medium having a different refractive index from that of the first medium is arranged at an interval corresponding to a wavelength of light. The photonic crystal owns a refractive index distribution which is changed periodically, and shows such a phenomenon (namely, superprism effect) in which refraction directions of light beams having slightly different incidence angles or wavelengths from each other are largely changed. The optical characteristics shown by the photonic crystal are described in detail, for example, in xe2x80x9cSuperprism phenomenon in photonic crystalsxe2x80x9d written by H. Kosaka et al., Physical Review B Vol. 58, No. 16, Oct. 15, 1998, and in Japanese Laid-open Patent Application JP-A-2000-66002.
Currently, various optical elements with employment of such photonic crystal as manufacturing materials thereof have been proposed. For example, Japanese Laid-open Patent Application JP-A-2000-56146 discloses such a self-waveguide circuit provided with photonic crystal on a major portion of a substrate so as to propagate a light beam within the substrate in the self-waveguide manner to separate the propagated light beam into a desirable number of light beams. Also, Japanese Laid-open Patent Application JP-A-11-271541 discloses such a wavelength separating circuit having the photonic crystal interposed between two claddings as materials so as to separate a light beam in correspondence with wavelengths of the components.
However, those conventional techniques disclosed in the above-mentioned documents are directed to the optical separating operations of the light beams. Therefore, those conventional optical elements/circuits cannot be utilized as, for instance, an optical deflection element for deflecting a plurality of light beams having different incidence angles or different wavelengths in different directions. As described above, no one could succeed in developing of optical elements, optical deflection elements, nor optical multiplexing elements which employ the photonic crystal as manufacturing materials thereof.
The present invention has been made to solve the above-explained problems. Therefore, a first object of the present invention is to provide an optical element for directing a light beam having a specific wavelength to a desirable direction by changing a propagation direction of the light beam in a wide range, without increasing an element size of the optical element, and furthermore, without increasing manufacturing cost thereof.
Also, a second object of the present invention is to provide an optical deflection element for deflecting light beams having different incidence angles or different wavelengths toward different emergence angles in a wide range, without increasing an element size of the optical deflection element, and furthermore, without increasing manufacturing cost thereof.
Furthermore, a third object of the present invention is to provide an optical multiplexing element for multiplexing light beams having different incidence angles with each other and emitting in the same direction, without increasing an element size of the optical multiplexing element, and furthermore, without increasing manufacturing cost thereof.
In addition, a fourth object of the present invention is to provide a scanning apparatus for scanning a light beam in a wide range at a high speed by causing a slight change in the incidence angle or wavelength, without increasing a size of the apparatus, and furthermore, without increasing manufacturing cost thereof.
To achieve the above-described objects, an optical element according to the present invention, comprises: photonic crystal having a refractive index which changes periodically depending on a location of the photonic crystal; wherein: an angle defined between a first end face and a second end face of the optical element is determined in such a manner that a light beam incident upon the first end face at a predetermined incidence angle and having a predetermined wavelength is emitted from the second end face in a desirable direction.
In the optical element, the photonic crystal may be provided between a first normal optical medium and a second normal optical medium.
Also, an optical deflection element according the present invention comprises: photonic crystal having a refractive index which changes periodically depending on a location of the photonic crystal; wherein: the optical deflecting element has a first end face and a second end face; and a shape of the second end face of the optical deflection element is determined in such a manner that a plurality of light beams incident upon the first end face at different incidence angles and having the same wavelength are emitted from the second end face in different directions corresponding to the incidence angles.
Alternatively, the shape of the second end face of the optical deflection element may be determined in such a manner that a plurality of light beams incident upon the first end face at the same incidence angle and having different wavelengths are emitted from the second end face in different directions corresponding to the wavelengths.
In the optical deflection element, the photonic crystal may be provided between a first normal optical medium and the second normal optical medium.
Also, an optical multiplexing element according to the present invention comprises: photonic crystal having a refractive index which changes periodically depending on a location of the photonic crystal; wherein: a shape of a first end face of the optical multiplexing element is determined in such a manner that a plurality of light beams incident upon the first end face of the optical multiplexing element at different incidence angles are optically multiplexed with each other along the same direction at a second end face of the optical multiplexing element.
In the optical multiplexing element, the photonic crystal may be provided between a first normal optical medium and a second normal optical medium.
Furthermore, a scanning apparatus according to a first aspect of the present invention comprises: an optical deflection element including photonic crystal having a refractive index which changes periodically depending on a location of the photonic crystal, the optical deflection element having a first end face and a second end face, a shape of the second surface of the optical deflection element being determined in such a manner that a plurality of light beams incident upon the first end face at different incidence angles and having the same wavelength are emitted from the second end face in different directions corresponding to the incidence angles; a light source for outputting a light beam having a constant wavelength toward the optical deflection element; and a resonant head for vibrating the optical deflection element, whereby a light beam deflected by the optical deflecting element is scanned with respect to an object.
On the other hand, a scanning apparatus according to a second aspect of the present invention comprises: an optical deflection element including photonic crystal having a refractive index which changes periodically depending on a location of the photonic crystal, the optical deflection element having a first end face and a second end face, a shape of the second surface of the optical deflection element is determined in such a manner that a plurality of light beams incident upon the first end face at the same incidence angle and having different wavelengths are emitted from the second end face in different directions corresponding to the wavelengths; and a light source for changing a wavelength of a light beam to be output toward the optical deflection element, whereby a light beam deflected by the optical deflecting element is scanned with respect to an object.
In the scanning apparatus, the photonic crystal may be provided between a first normal optical medium and a second normal optical medium.